As shown in FIGS. 1 and 2, a V-type engine 1 is generally formed with lateral banks 3 for arrangement of a plurality of cylinders 2 laterally oppositely with predetermined angles, each of the cylinders 2 having therein a piston 4 for reciprocating motion, motive energy of the pistons 4 being transmitted through connecting rods 5 to a crankshaft (not shown).
Portions of a sliding surface in the cylinder 2 for the piston 4 which receive more and less lateral pressures by rotation of the crankshaft are referred to as thrust and anti-thrust load side portions 2a and 2b, respectively. In FIGS. 2 and 3, with the crankshaft being rotated in a clockwise direction, the thrust load side portions 2a are lower and upper sides of the left and right cylinders 2, respectively; the anti-thrust load side portions 2b are upper and lower sides of the left and right cylinders 2, respectively.
As shown in FIG. 2, provided in the cylinders 2 at upper portions 2c between the lateral banks 3 are a plurality of lubricating means 6 for cooling of the pistons 4. Each of the lubricating means 6 comprises, as shown in FIG. 2, a cooling jet 8 with an injection nozzle 7 directed to a skirt 4a of the piston 4 and an oil subhole 9 for formation of a flow passage in the upper portions 2c of the cylinders 2 so as to supply oil to the cooling jet 8. In a further example of the lubricating means 6 shown in FIG. 3, they are arranged in sides 2d of the cylinders 2 and each comprises the cooling jet 8 with the injection nozzle 7 directed to inside of the piston 4 and the oil subhole 9 in the side 2d of the cylinder 2 so as to supply oil to the cooling jet 8.
The skirt 4a of the piston 4 is formed with a notch 10 for prevention of contact with the injection nozzle 7 of the lubricating means 6 during sliding motion of the piston 4 in the cylinder 2. In the example shown in FIG. 2, the notches 10 are formed adjacent to the upper portions of the cylinders 2 (at upper positions); in the further example shown in FIG. 3, the notches 10 are formed adjacent to the sides of the cylinders 2 (at lower positions).
When the pistons 4 are to be cooled in such lubrication structure, oil is passed via the oil subholes 9 and the cooling jets 8 and is injected by the injection nozzles 7 into the pistons 4.
Conventional art as engine lubricating means is disclosed, for example, in the below-mentioned References 1 and 2.                [Reference 1] Japanese utility model laid-open publication No. 2-27144        [Reference 2] JP 6-101473 A        